The present invention relates to a method for the adjustment and control of a device serving to cut strip material in a manufacturing machine.
Whilst reference is made throughout the present specification to the field of cigarette manufacture and in particular to filter assembly machines, that is, machines by which filter tips are applied to cigarettes, no limitation of the general scope of the invention is implied by the selection of such an example.
Conventionally, the manufacture of filter tipped cigarettes involves fastening together pairs of axially aligned plain cigarettes, interconnected by a filter of double length, with a gummed band of material; once firmly stuck, the assemblies thus created are cut through half way along their length to give two single filter cigarettes each. The bands in question are severed in succession from a steadily moving continuous strip of paper material by means of a cutting device.
The prior art embraces cutting devices (disclosed in UK patent 2 123 737) comprising two rollers counter-rotating about parallel axes, each of which is fitted with a plurality of uniformly distributed blades.
Each blade of one roller pairs with a corresponding blade of the other roller to create a scissor type cutting mechanism. Thus, as the two rollers rotate, the blade of the one enters into tangential contact with a corresponding blade of the other and effects a progressive cut through the strip.
The adjustment of each pair of blades is effected manually in devices of this type, verifying that contact between the two blades, which occurs at one point transferring progressively from end to end, is maintained along the full length of the cutting edge as the rollers rotate.
It has been found, however, that in addition to an initial adjustment, further corrections need to be made to the position of the blades once the filter assembly machine is in operation.
More exactly, with the gradual rise in temperature of the machine during operation, expansion occurs in the cutting device, and more especially in the means by which the rollers are supported, of which the ultimate result is a mutual distancing of the axes of the rollers, hence part or total separation of the cutting edges of each pair of blades.
The upshot of such a contingency is that contact can fail to occur between the blade edges and the continuous strip material, and the strip therefore does not separate into discrete bands as required. On the other hand, an initial adjustment designed to take account of the effects of distancing caused by thermal expansion would lead to a destructive action on the cutting edges of the blades during the initial stages of operation.
The object of the invention is to provide a method such as will overcome those drawbacks attributable to thermal expansion which affect cutting devices of the type thus described during their operation.